1. Field of the Invention
The present invention relates to an improved pen nib of a writing instrument, particularly a pen nib made of a hard material such as hard plastics, metals or ceramics.
2. Description of the Related Art
Plastic pen nibs are well known and many patents have been granted for such plastic pen nibs. Most pen nibs are produced by an extruding method using a perforated die or a binding method whereby preproduced plastic filaments are bound to form capillary passages. Both of these methods produce a pen nib having plurality of ink capillary passages formed therein, and all of such passages are axial hollow extensions open axially at the head of a longitudinal plastic pen nib. The head is worked to have a round or shaped profile in a subsegment process, as desired.
JP-B 49-2132 (Japanese Examined Patent publication), for example, shows dies for use in such an extruding method, and various patterns of axially extending capillary ink passages with openings formed at the nib head. Each opening has the same profile or pattern as that of the axially extending passage, when the nib is seen in the axial direction, i.e., in an axially front view of the longitudinal nib.
U.S. Pat. No. 3,558,392 and EP 82,206 disclose the binding methods with plastic filaments of producing pen nibs, each having axially extending capillary ink passages with openings formed at the nib heads. Each passage of a nib has the same profile as that of its outlet or opening in a front view of the nib, as in the above JP reference.
Recently, there is an increased demand for pen nibs for high speed writing instruments used in plotters automatically indicating detection outputs or in drawing apparatuses.
Such a high speed writing pen nib must, of course, have a wear resistance against paper as the pen nib is in intermittently contact with and slides over the paper surface at a high speed.
In this regard, JP-A-60-112497 discloses a wear pen nib of metal for use in a dot type printer or various recording devices, which are kinds of plotters. Powder metal with a water solvable salt such as sodium chloride is pressed in a mold to form a nib blank, and the metal blank is sintered with the result that the sintered nib has randomly arranged perforations formed in the entire body, which, in combination, form many capillary passages therein. This nib is similar to a conventional pen nib of a felt block. The above sintered metal nib and the conventional felt nib do not have axially straight ink passages formed artificially, but have only naturally formed ink passages in the form of random perforations or the like.
JP-A 1-146797 also describes inorganic wear pen nibs of metals or ceramics. Powder of the wear material is press-formed in a mold and sintered to form a nib having a plurality of molded ink passages, each extending axially and completely opening axially or straight forwardly opening at the nib head.
Therefore, the disclosed inorganic pen nibs are common to those of the above mentioned conventional extruded or bound plastic pen nibs in that each axially extending capillary ink passage has the same profile as that of its opening or outlet formed at the nib head, in an axially front view of the nib, with the same size.
With respect to the high speed writing with the wear pen nib, the inventors recognized that the conventional wear pen nib is apt to scratch the paper, with the result that the surface of the paper is damaged, and that dust produced from the paper is apt to enter the passage openings at the nib head and clog them. As a result, there is a tendency for the wear nib pen to be unable to continue a smooth and good writing performance. That is, with the wear nib pen, the dust prevents the ink from flowing out smoothly from the openings, even if it does not clog them all, with the result that lines, letters or the like written by the ink on the paper become blurred, i.e., the pen becomes scratchy. Further, the writing resistance is increased relative to the conventional plastic pen nib due to the hard edges of the passage openings. The conventional plastic pen nib is plastically deformable, and thus its passage openings have soft edges in comparison with those of the wear nib.
A hard resin pen nib made of a thermosetting resin molded to have capillary ink passages and openings, with profiles similar to the conventional ones, exhibits substantially the same poor writing performance, when used for a high speed writing, as that of the inorganic pen nib, even though the hard resin pen nib may have a lower wear property than the inorganic nib.
It is noted that a pen nib having no coaxial opening, such as those shown in FIG. 2 of JP-A 146797 and in FIG. 6 of JP-B 49-2132 mentioned above, exhibits less writing resistance than the other nibs having a coaxial passage opening, i.e., a central outlet formed in the head at a central area of the head surface. This is because the edge of the coaxial opening is apt to scratch a paper during writing, but the central surface area having no opening exhibits no substantial resistance to the paper, so long as the head forms a smooth round central surface.
In a low speed writing, such a scratching tendency does not cause a paper to be damaged and to produce dust to a substantial extent in practice, and such a coaxial opening is advantageous in ensuring a smooth and continuous ink supply onto the paper. This is because no coaxial opening causes the area effective for allotting a desired pattern of peripheral passage openings to be reduced and limited in scope in the entire top head surface.
Even with the same entire opening area (i.e., areas of plural openings) between the non coaxial opening case and the coaxial opening case, the coaxial opening case is able to write a line having a narrowed width with a better ink flow, although the performance is definitely influenced by a capillary action of the ink passages formed in the nib body.
Further, in comparison with a conventional coaxial opening case having a coaxial opening and peripheral openings, a conventional non-coaxial opening case having only peripheral openings equivalent to those of the coaxial opening case is, as a matter of course, inferior to the coaxial opening case in respect of the ink supply ability thereof.